1. FIELD OF THE INVENTION
This invention relates to electrical contact structures having electrically conductive probing members such as fingers, needles, or the like, that make electrical contact with an item to be probed. More specifically, the invention relates to electrical probes for use in measuring and testing electronic devices with a multiplicity of contact elements or points. The invention has particular utility as a Kelvin probe, that is, a probe adapted for sensing two or more electrical parameters present at a single point in the electrical circuit of the device or body to be probed.
2. Description of the Prior Art
The testing of the electrical parameters of fragile, miniature semi-conductor devices such as tunnel diodes, transistors, integrated circuits, and the like, requires the use of very delicate and reliable equipment which will not damage the device being tested. The substrates of these devices which are contacted by a probe during the testing are typically 1/4 to 1/2 mil thick, have lengths and widths of 25 mils, may have ball terminals which are 20 mils in diameter and spaced 15 mils apart. It is therefore necessary that any probe have compatable dimensions in order to unambiguously sense the particular electrical parameter desired at the particular point in the electrical circuit selected. The use of Kelvin probes has become standard in the industry in order to substantially eliminate any error in the sensed parameter due to contact resistance and lateral spacing between probe ends. A typical Kelvin probe together with a discussion of the technique used in testing the electrical parameters of a device with a Kelvin probe is to be found in U.S. Pat. No. 3,609,539.
Since the contact areas on the electrical devices to be probed are of such small dimensions and typically fragile, it is necessary that the probe come in contact with the contact areas in such a manner as will not damage or destroy the device to be probed. Any cracking or breaking of a contact area or ball terminal may destroy the device as well as give erroneous readings of the electrical behavior of the device. Particular difficulty has been experienced with lateral components of forces exerted by probe of the test equipment making engagement with the contact areas and ball terminals, leading to gouging of substrate surfaces and shearing off the ball terminal. It is necessary, however, that sufficient force be applied between the probe and the contact area to assure a good electrical connection, yet still without damaging the device.
Previous attempts at solving this problem have centered on designing Kelvin probes having a self-centering feature such as is found in U.S. Pat. No. 3,609,539. The Kelvin probes are then typically received in gimbaled mountings which permit motion of the probe so as to prevent the contact and shearing forces from becoming unacceptably large. An example of such a mounting is discussed in IBM Technical Disclosure Bulletin, Vol. 7, No. 6, November 1964, pages 444-445. While the gimbaled mountings of the Kelvin probes together with the use of self-centering features has met with some success, damage to the device to be probed continues to occur with such frequency as to require the development of yet further improvements which would reduce the possibility of damage to the device.
Another example of a Kelvin probe is to be found in IBM Technical Disclosure Bulletin, Vol. 13, No. 11, April 1971, page 3365.